sediments. Sand caps are more visually 

 and chemically distinct than silt caps. The 

 quantity of mixing during dredging 

 operations has been directly addressed in 

 recent coring investigations (Section 4.0), 

 and the results suggest that silt caps may 

 induce less mixing with mound material 

 than sand caps. These results do not 

 suggest that silt caps are more effective at 

 containing contaminants. It is possible that 

 more sand material than silt is required to 

 form an impervious cap. 



A DAM OS computer model has been 

 developed as a tool for planning and 

 managing disposal operations. This model 

 predicts the configuration of a capped 

 mound and aids in estimating the amount 

 of capping material required to isolate any 

 contaminants in that mound (Appendix A). 

 By predicting mound radii and capping 

 volumes for a given amount of dredged 

 material, the model helps NED managers 

 plan appropriate capping ratios. 



Evaluations of early capping operations 

 highlight the requirements for operational 

 success, including pre-project planning, 

 accurate navigation, and careful record- 

 keeping. In reviewing the historical 

 record of the NED capping projects, the 

 focus will be on "lessons learned" because 

 this information is valuable for any future 

 capping efforts. 



2.1 Central Long Island Sound 

 Disposal Operations 



This report describes four capping 

 projects conducted in the Central Long 

 Island Sound Disposal Site (CLIS): 



Stamford-New Haven, Mill-Quinnipiac 

 River, Norwalk, and the two Experimental 

 Cap Sites. These are the most 

 comprehensive and best-documented of all 

 the capping projects conducted by the 

 NED. In addition, they were the only 

 early capping projects in which specific 

 capping material was prescribed. The "de 

 facto" method mentioned above, in which 

 the contaminated material was dredged and 

 deposited before less contaminated 

 material, was used in many other capping 

 projects (e.g., Portland, Brenton Reef, 

 New London, other capped mounds at 

 CLIS; Bajek et al. 1987). 



Each of the CLIS capping operations 

 will be discussed in historical progression 

 to establish what factors influenced the 

 degree to which the project was or was not 

 successful. This linear account serves as a 

 valuable record of the early capping 

 operations and provides a checklist of 

 recommendations for future capping 

 projects. 



All the capped mounds formed as a 

 result of these four projects are located 

 within the boundaries of CLIS. This 

 5.2 km 2 (2 nm 2 ) area is located 

 approximately 10 km south-southeast of 

 New Haven, Connecticut (Figure 2-1). 

 Water depths over the disposal site range 

 from approximately 17 to 25 m. 



CLIS lies within one of the most 

 intensively studied regions of Long Island 

 Sound. Detailed oceanographic studies of 

 the area began in the 1950s with the 

 pioneering work of Gordon Riley and his 

 co-investigators at Yale University's 



Sediment Capping of Subaqueous Dredged Material Disposal Mounds 



